This fixes the following kind of ICE on configurations with zero
overhead loops support:
../src/pjlib-test/thread.c: In function 'thread_test':
../src/pjlib-test/thread.c:328:1: internal compiler error: in
dwarf2out_var_location, at dwarf2out.c:21846
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>